Hey Beetlegator, here's what I've been able to find out. I went on Club Getaway's Feb/05 cruise, & they had a sold out total of approx 275 guests. I've spoken to others who've been only on singlescruise.com cruises. They have also had a similar fun experience.
From all information until now, I surmise that both experiences will be great. I fugure that Club Getaway has more 20 something yr. olds, because it's emphasis is on outdoor sports. Therefore it attracts more of your "weekend backpack" types...which tend to be younger, at least in the female category.
Any further experiences could change this assumption.